Dehydrating process



' A g 1942- J. c. IRWIN, JR 2,292,447

DEHYDRATING PROCESS Filed. April 22, -1941 gvwemiom;

James C. Z7tca,in,Ji:,

mhh M Patented Ao ,11,1942 I 2 292 447 .7 'i yazazdivjfff o f t I IF-a-I Y James-CJrwin; J12; Kansas City Mog assignor to I -Unitc'd States Cold Storage ,corpol ati miiwil mington, Del a corporation of llelztwa 'e, nd

t D. C, Pfei fl er and J; M Hill both'of; Dallas Tex This invention relates to a process for cold'f'room or placed in' thejvacuumfchamber food products and to the'productobtain'ed from of the machineand 'afterbeing-subjected to a practice of this process. g 1 1 a relatively low*pressure' may befrozenf inap- The fundamental process'comprehends freezproximately one-half -hours time" by evaporaing any food product containing a large moporticnof theater i'romthe potatoes-i; Thev'a'cu-- tion of water and subjecting such frozen food um is maintairiedat such apressurefas willcause substances to a low pressuresufiicient to cause the'potatoes to freeze at a temperature about the ice to evaporate or sublime directly into wa- 2 0'tOi25? F 'an'd"afterfreezingQthe potatoes are ter vapor. maih'taihdat this"temperature for-approximate- It is well known that certain materialsiconl0 1y 24 hours, duringwhich time the largest part taining'a large percentage of water can bedried 'of lwater {evaporate fIhepotatoesinipans in this manner and the present invention resides areplacedoni the trayis'pr suppcrting'shelves" I! in an improvement on the priora'rt methods 1 in thefvacuumchamber]lg g V The drawing discloses'a diagrammatic form of The shelvesi are allow-to receive-the heat an apparatus which may be'used to perfo'rm the l5 ingfinediiim which supplied*through inlet herein disclosed process. .7 header Is and the flowof thisfluidis controlled The typical products dried by this process are by an inletvalvel V f The individual shelves are off e whites, milk, potatoeaye' s etc, "Th each conne ted theinletjheader l3; and the food or other product to be dried is frozen inany heating "fluifdfw Q F {will the i let J3 ug suitable manner as by placing itfin a coldstorage 20 t e g t t q q5 ea 'Theihatin'g room or by disposing the material in the vacuum ar e ms rt chamber of the dryingfapparatus. In either flow i t m," "In th p t'i gt h method, the food, is frozen solid in a relatively wh i pm; 9 5, h ting dried {the hgatifig fluid thick layer either by the loss of heatinjthe I cold chamber or by the evaporationo f water The potgtoes g i t I from the food itself in the vacuum chamberof I gm r gt flbetw'eeni8 mm; to 1.5 the machine. h f mm; by ,th e'apparatusdescribed hereinafter; At The frozen food product is then placed on suitf gum' fi a ta g t t-3 1 mable supporting means in the vacuum chamber ti 'df'th'p t tdgs gt'approximately 2013 and is subjected simultaneously to a high degree pg' ithe lgyf is chncg completeiy driedin-about of vacuum and the addition of heat which causes 241 6111 that"tirne,,the temperature of the the ice to sublime, the supply of heat being re pot t es ill he a d 'e explained i tnggqulated to an amount equal to the loss of heat cc,- ditibn t ng; qp qt the y r; 01: p i casioned by the evaporation or sublimation 0f t e 'flu 'egitfigfe idfl' n tu tb be m re rap the ice in the food product. 'The evaporation my' gap ra Th yin' giis cdn'tjnuedat thi and heating is continued until approximately 95 Y 7 v h ljmpfgtujt m tm f rmam ing to 98 per cent of themoisture containedin the r' idu pmdsmr j food product is removed, at which point the rate h 1 of cooling occasioned by the evaporation of the vg um;t e cu jm'ch mber;ll i connected by ice becomes somewhat slower. When this stage 1 5115 {,5 thehamber "l1 which contains the vacuum In 'ordei' to' 'maintain' the? ii'eiiuirc j deg ee or of the drying process is reached, the tem at e a large body or silica gel 18. The' chamber n of the product being dried'begins to rise above a. v ha any suitable conven on ivwuumfprddliclnfl freezing temperature and as the degree of heat n [9" edfine 'tedthereto by pipe 2,0, for r supplied to the food product is continued at subrfidvmglfairgzand Qther iv-porisj fi'omltfnechamber stantially the same level, during the finalstages nuwhichlare nqt comvlgns'ed bythe silica gelk A misture remaining in the f P L is I Q h" and a valve 22: is associated. withttheiniet'zo to w-35 the gg ggg g g fggg gggg the-mum pump. been. the' silica gel, is Subs n 1 y equa l8 iscool'edbymeans of a coil 23-havinganinlet ra 'idl removed. l V v fs g ty p i cfi il eiiifig gi ggg gthgi f p 24 and outlet 25 through WhlCh a. cooling mediforming the present inventicimblanched potatoes may be sliced approximately three-eighths of an inch thick and the slices are placed in a pan |0 in a single layer.' The potatoes may be frozen um is circulated to absorb'the heat liberatedi in therein as be: explainedbelow. 1 The chamber I 1 may'have a suitablepressure gage 26 connectthe silica gelwhen' the' wateryapor condensesed thereto and a thermometer 21 is operatively associated with the body of the silica gel.

The operation of this apparatus is as follows: The potatoes after being frozen in trays l and disposed in the vacuum chamber II, are subjected to a vacuum when the operation of pump I9 is initiated. After all the air and other noncondensable gases are removed from the chamber ll, conduit [6, and chamber l1, the pressure is reduced to approximately .80 mm. to 1.5 mm. at which pressure the ice in the frozen potatoes will be evaporated directly to water vapor and conveyed through conduit [6 to the body of silica V gel l8. As soon as the water vapor contacts the silica gel, it is condensed to a liquid of much smaller volume than the vapor to maintain the low pressure already established. As the water in the form of ice evaporates from the potatoes, the food is cooled and therefore to prevent the temperature falling below 20 to 25 F., heat is supplied to the .layer of potatoes by circulating a fluid at approximately 60 F. through the shelves I2 upon which the trays of potatoes aredisposed. The quantity of heated fluid circulated is just suflicient to supply the amount of heat necessary to make up for the cooling caused by evaporation and the water is controlled by valve l4.

In the example given, the potatoesare subjected to this reduced pressure and below freezing temperature for a period sufficient to remove the most of the contained water. Then the temperature is raised to remove the residual moisture.

The point at which the rate of cooling caused by the evaporation of moisture from the food drops off quite materially, as evidenced by the temperature rise, is a characteristic point and is found in all materials containing a large percentage of water and dried in accordance with the present teachings. If the product is not maintained below a freezing temperature until this point is reached, it has been found that the dried food cannot be reconstituted by the mere addition of water to have all the original properties of the food. However, if the temperature is maintained below freezing until this point is reached, the temperature may be raised during the remainder of the drying process without detrimental results to the .dried food, this rise in temperature being sufficient to cause a rapid evaporation of the residual 2 to 5 per centof moisture within a much shorter period than has ever been known to the prior art. After this characteristic point is reached, in any material being dried, its temperature may be raised to the temperature of the heating fluid to effect the removal of the residual moisture without any change in the ability to reconstitute the dried food product,

The specific example given above as applied to potatoes may be duplicated to remove large quantities of water from any food product. The specific temperature conditions and time of drying may be varied, but the same principles will be found to apply to all such products and the characteristic point at which the temperature is raised, will be always encountered at that stage in the drying process when substantially all of the water has been removed.

With any product, the material may be frozen in a cold room or by evaporation in the vacuum chamber II and the freezing may be rapid or slow, the rate of freezing apparently not being important in the final product. In the drying of all foods, the temperature of the food is raised in the-final stages to accomplish the more rapid removal of the residual moisture.

Egg whites dried in accordance with this process may be rapidly reconstituted by the addition of an appropriate amount of water and the reconstituted product is comparable in all respects to fresh egg whites. The reconstituted whites may be whipped to a froth and may be used in cooking recipes and for all other uses of a fresh egg white. A notable example of the ability of the egg white dried in accordance with this teaching to be used as distinguished from egg whites dried by prior art methods is that the present product may be used in making an angel food cake which use cannot be made of any of the other known dried egg products.

The egg white dried by this process may be stored for any length of time without the previous fermentation of the prior art methods and it also lacks the characteristic odor of driedegg albumen of the previously dried materials. Again, it may be reconstituted very rapidly as distinguished from the long period of reconstitution required with the old dried egg whites.

Coffee which has been brewed according to the conventional methods may be subjected to the drying process of this invention and the dried material is highly resistant to caking, is immediately soluble in water, and has been found to retain the aroma and taste of the original brand used in brewing the coffee. It is preferred to concentrate the coffee by conventional methods before subjecting it to the present drying process. However, this is unimportant as faras the characteristics of the final product are concerned, and is done merely to save operating expenses in removing the large quantities of water present in the coffee drink.

Spinach may be dried by this process, being first blanched, the fresh whole leaf is frozen and subjected to the vacuum removal of moisture.

The final product has a pale green color and a characteristic odor.

this process may be stored indefinitely then reconstituted to hav its original levening properties. When compressed'yeast is stored for any period it loses its potency day by day and by the end of seven days it has lost a great part Of its efficiency. The dried yeast product of this invention may be stored for apparently an indefinite period without regard to temperature conditions, and yet may be immediately revived to have its original properties, the organisms apparently remaining in a dormant state. The ordi nary compressed yeast of commerce, is quite sensitive to freezing and thawing and can be made useless by passing through this cycle and if subjected to a relatively high temperature, as normal summer temperature, for any length of time, its potency decreases rapidly. However, the yeast dried by the present process shows no damage when subjected to freezing temperatures followed immediately by warming to room or the relatively high temperatures that destroy the ordinary compressed yeast. Further, the dried yeast of this invention may be stored indefinitely at this relatively high temperature without perceptible damage.

The above examples have been given merely to demonstrate the use of the process, it being obmany similar products can be subjected to the process. These examples are not intended to limit the invention beyond the scope of the following claims.

I claim:

1. The method of drying a food product containing water comprising freezing said product,

thereafter raising the temperature of said frozen product while the residual water is being removed,

3. The method the residual water is being removed.

5. The method of drying a food product containing water comprising freezing said product, subjecting said-frozen product to a vacuum eiTee least F. while said residual water is being removed.

6. The method ofdrying a food product con.- taining water comprising freezing said product,

product to a pressure being said frozen product at least 2 F. below its freezing temperature ,Whlle said large percentage of water is removed, and thereafter raising the temperature of said product to at while said residual water is being removed.

JAMES C, IRWIN, JR. 

